Toxoplasma gondii apical membrane antigen-1

ABSTRACT

The invention provides polypeptide fragments derived from TgAMA-1, nucleic acids that encode the polypeptide fragments, and TgAMA-binding polypeptides such as antibodies. Methods for using the polypeptide and nucleic acid molecules to produce vaccines are also provided. In addition the invention provides methods involving use of the polypeptides, nucleic acids, and binding polypeptides, such as antibodies, for the prevention and treatment of Toxoplasmosis.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.60/247,870, filed Nov. 9, 2000, the entire contents of which is herebyincorporated by reference.

GOVERNMENT SUPPORT

This invention was made in part with government support under grantnumber R29A142355 from the National Institutes of Health (NIH). Thegovernment may have certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to TgAMA-1, and TgAMA-1-based animal andhuman vaccines for toxoplasmosis.

BACKGROUND OF THE INVENTION

Toxoplasmosis is among the most common parasitic diseases of man.Serosurveys suggest prevalence rates as high as 70-90% in many areas ofboth the developing and developed world. Between 10-45% of Americansbecome infected at some point in their lives. An infection in anindividual with a competent immune system generally has minor or nosymptoms. The infection tends to be self-limiting, with the individual'simmune system controlling and eliminating most of the parasites. Someparasites remain in bradyzoite form following acute infection and willbe present in cysts in the central nervous system and muscle throughoutthe remainder of the individual's life.

In contrast to the mild clinical symptoms of infection seen in a healthyindividual with an intact immune system, subjects with weakened orotherwise compromised immune systems can have serious clinical effectsfrom toxoplasma infection. In the fetus, toxoplasma infection can causemental retardation, visual defects, and death. Toxoplasma infection cancause neurological damage, ocular lesions and death in adults withcompromised immune systems, a group which includes for exampleindividuals with HIV infection or patients undergoing immune-suppressivetreatment for cancer.

Acute toxoplasmosis can be difficult to treat.Sulfadiazine/pyramethamine is a regimen of choice, although side effectsserious enough to warrant discontinuation of treatment are common. Thetoxic and potentially teratogenic effects of this regimen makemanagement of the pregnant woman particularly problematic. AIDS patientsrequire lifelong suppressive therapy to prevent relapse, and a many asone third of the patients receiving suppressivesulfadiazine/pyrimethamine therapy cannot tolerate the adverse sideeffects. For those who can tolerate the drugs, relapse occursfrequently. Pyrimethamine/clindamycin is a useful alternative therapy inAIDS patients who suffer an unusually high frequency of side effectsfrom sulfa drugs. Unfortunately, this alternative combination can alsocause considerable toxicity and is less effective at preventing relapse.Prevention of transmission through vaccination would be preferable totreatment, particularly for pregnant women and the immunocompromised.

SUMMARY OF THE INVENTION

According to one aspect of the invention, isolated TgAMA-1 polypeptidemolecules are provided. The TgAMA-1 polypeptide molecules includeantigenic fragments of the polypeptide sequence set forth as amino acidsSEQ ID NO:1.

According to another aspect of the invention, fusion proteins areprovided that include the foregoing antigenic polypeptide.

According to another aspect of the invention, isolated TgAMA-1 nucleicacid molecules are provided. The TgAMA-1 nucleic acid molecules areselected from the group consisting of a fragment of the nucleotidesequence set forth as nucleotides 1-2507 of SEQ ID NO: 2 between 12 and2506 nucleotides in length, and complements of (a), wherein the fragmentencodes the foregoing isolated TgAMA-1 polypeptide.

According to another aspect of the invention, expression vectors areprovided and include the isolated foregoing TgAMA-1 nucleic acidmolecule operably linked to a promoter.

According to another aspect of the invention, expression vectors areprovided and include an isolated nucleic acid molecule of SEQ ID NO: 2.operably linked to a promoter.

According to another aspect of the invention, host cells transformed ortransfected with the aforementioned expression vectors are provided. Insome embodiments, the host cell is an insect cell. In certainembodiments, the insect cell is a High Five™ cell.

According to another aspect of the invention, a transgenic non-humananimal that includes the foregoing expression vector are provided. Insome embodiments, the transgenic non-human animal expresses a variablelevel of TgAMA-1. In certain embodiments, the transgenic non-humananimal expresses an antigenic fragment of SEQ ID NO: 1. In someembodiments, the transgenic non-human animal is a mammal. In certainembodiments, the transgenic non-human animal is a bovine.

According to another aspect of the invention vaccine compositions areprovided that include the foregoing isolated TgAMA-1 polypeptide and anadjuvant.

According to yet another aspect of the invention, vaccine compositionsare provided that include TgAMA-1 or a functionally active variantthereof, and an adjuvant.

In some embodiments of the foregoing vaccine compositions the vaccine isa proteosome vaccine. In certain embodiments of the forgoing vaccinecompositions, the adjuvant is selected from the group consisting of:mineral gels, e.g., aluminum hydroxide; surface active substances suchas lysolecithin, pluronic polyols; polyanions; peptides; alum, MDP,N-acetyl-muramyl-L-threonyl-D-isoglutamine (thr-MDP),N-acetyl-nor-muramyl-L-analyl-D-isoglutamine, andN-acetylmuramyl-L-alanyl-D-isoglutaminyl-L-analanine-2-(1′-2′dipalmitoyl-sn-glycero-3-hydroxyphosphroyloxy)-ethylamine,monophosphoryl lipid A; saponins (QS21; DQS21); QS-7, QS-17, QS-18, andQS-L1; incomplete Freund's adjuvant; complete Freund's adjuvant;montanide; vitamin E, oil emulsions, and various water-in-oil emulsionsprepared from biodegradable oils such as squalene and/or tocopherol.

According to some aspects of the invention, methods for immunizing asubject are provided. The methods include administering to the subjectan effective amount for immunizing the subject, of the foregoingvaccines. In some embodiments the subject is a mammal. In certainembodiments the subject is a human. In some embodiments, the subject isat risk of infection from Toxoplasma gondii. In some embodiments, thesubject is a mammal. In certain embodiments, the subject is a human.

According to another aspect of the invention, TgAMA-1 bindingpolypeptides that selectively bind to the foregoing isolated TgAMA-1polypeptide are provided. In some embodiments, the TgAMA-1 bindingpolypeptide is an antibody or antigen-binding fragment of an antibody.In certain embodiments the antibody or antigen-binding fragmentspecifically binds to a region comprising about 12 or more cysteineresidues of the forgoing isolated TgAMA-1 polypeptide. In certainembodiments, the binding polypeptide blocks entry of Toxoplasma parasiteinto a cell. In some embodiments, the TgAMA-1 binding polypeptide is amonoclonal antibody. In certain embodiments, the TgAMA-1 bindingpolypeptide is a humanized monoclonal antibody.

According to another aspect of the invention, anti-idiotype antibodiesthat selectively bind to the TgAMA-1 binding polypeptides are provided.

According to yet another aspect of the invention, methods for treating atoxoplasma infection are provided. The methods include administering toa subject in need of such treatment, an effective amount of theforegoing TgAMA-1 binding polypeptides to treat the toxoplasmainfection. In some embodiments, the TgAMA-1 binding polypeptide blocksthe entry of Toxoplasma parasite into a cell. In some embodiments, thesubject is a mammal. In certain embodiments, the subject is a human.

According to yet another aspect of the invention, methods for reducingthe likelihood of a toxoplasma infection are provided. The methodsinclude administering to a subject in need of such treatment, aneffective amount of a foregoing TgAMA-1 binding polypeptide to reducethe likelihood of toxoplasma infection. In some embodiments, the TgAMA-1binding polypeptide blocks the entry of Toxoplasma parasite into a cell.In some embodiments, the subject is a mammal. In certain embodiments,the subject is a human.

DETAILED DESCRIPTION

The invention relates in some aspects to a Toxoplasma gondii tachyzoiteprotein termed TgAMA-1. TgAMA-1 is relatively homologous to theextensively studied apical membrane antigen-1 (AMA-1) family of proteinsof malaria parasites. In animal models of malaria, passive immunizationwith polyclonal antibodies against AMA-1, or immmunization with nativeor recombinant renatured AMA-1, protect against parasite challenge;AMA-1 is currently under investigation as a vaccine candidate for humanmalaria. The antigenicity of malarial AMA-1 resides in its extracellulardomain, with which TgAMA-1 shows a high degree of structuralconservation. The present invention relates to the use of recombinantTgAMA-1 and its extracellular domain as vaccines for toxoplasmosis. Theefficacy of TgAMA-1 as a vaccine is readily confirmed by administeringTgAMA-1 and/or vaccine formulations comprising TgAMA-1 to test animals,such as mice. Cats and sheep (important animal reservoirs ofToxoplasmosis) are also readily tested to confirm the vaccine potentialof TgAMA-1, as well as ultimately, humans.

As used herein, the term “TgAMA-1” means human Toxoplasma gondii apicalmembrane antigen-1. As used herein the term TgAMA-1 molecules includesTgAMA-1 polypeptides, TgAMA-1 nucleic acids, and polypeptides, such asantibodies, that bind to TgAMA-1 polypeptides described herein.

As used herein a “subject” shall mean a human or vertebrate animalincluding but not limited to a dog, cat, horse, cow, pig, sheep, goat,non-human primate (e.g. monkey), rabbit, rat, mouse, and bird. The term“subject” also includes cells collected from a human or animal, forexample, blood collected for purposes such as, but not limited to,transfusions.

As used herein, the term “cell” means a cell capable of being infectedby, or suspected of being exposed to Toxoplasma. This may include cellsfrom a subject and cells grown in culture. In some embodiments, a cellmay be a control cell, which has not been exposed to toxoplasma. Celltypes may include, but are not limited to, neuronal cells, ocular cells,erythrocytes, and intestinal cells.

As used herein, the terms “toxoplasma infection”, and “toxoplasmosis”refer to infection by all members of the genus Toxoplasma. Theapplication of the invention is described in many cases with referenceto Toxoplasma gondii parasites, and is intended to include applicationof the methods to all strains Toxoplasma gondii. The methods of theinvention are also envisioned to apply to treatment of toxoplasmaparasite infections that result from other toxoplasma species.

Particularly important subjects to which the present invention can beapplied are subjects having been or suspected of having been exposed totoxoplasma, which includes subjects diagnosed with infection, exhibitingsymptoms of infection, or having known or probable risk of exposure totoxoplasma infection.

A subject may or may not exhibit symptoms of infection such as fever,swollen lymph glands, muscle aches, and pains. Methods to diagnosesymptomatic and asymptomatic toxoplasma infection are known to those ofordinary skill in the medical arts and include, but are not limited to,blood tests for antibodies to the toxoplasma parasite. Brain scans bycomputerized tomography (CT scan) or magnetic resonance imaging (MRIscan) may also be used in the diagnosis of toxoplasma infection.

Treatment as it relates to the invention may be prophylactic ortherapeutic.

Prophylactic and therapeutic treatment may involve administering avaccine to induce/augment an immunoprotective response, or a polypeptidesuch as an antibody that binds TgAMA-1, to interfere with the toxoplasmaparasite in the subject. Thus, in an important embodiment, the antibodyto TgAMA-1 is administered to inhibit infection in a subject. As usedherein, the term “reduce likelihood of infection” means to reduce orlower the level of entry into cells by the toxoplasma parasite. To“inhibit” or “block” may also mean to prevent entry into the cells bytoxoplasma, but it is not necessary to prevent all entry to lessen orprevent the manifestation of disease.

As used herein the term “TgAMA-1 polypeptides” means the polypeptide setforth as SEQ ID NO: 1, variants of the polypeptide set forth as SEQ IDNO: 1, and fragments of the polypeptide set forth as SEQ ID NO: 1. Asnoted above, the invention provides isolated TgAMA-1 polypeptides andTgAMA-1 binding polypeptides, such as antibodies, that bind to TgAMA-1polypeptides. The invention also embraces functional variants, such asfragments, of the TgAMA-1 polypeptides. As used herein, a “functionalvariant” or “variant” TgAMA-1 polypeptide is a molecule that containsone or more modifications to the primary amino acid sequence of theTgAMA-1 polypeptide and retains the antigenic function of TgAMA-1.Modifications that create a TgAMA-1 polypeptide functional variant canbe made, for example, to enhance a property of an TgAMA-1 polypeptide,such as peptide stability in an expression system or the antigenicity ofthe TgAMA-1 protein; or to provide a novel activity or property to aTgAMA-1 polypeptide, for example, to enhance detection. Modifications toa TgAMA-1 polypeptide can be made to a nucleic acid that encodes thepeptide, and can include deletions, point mutations, truncations, aminoacid substitutions and additions of amino acids. Alternatively,modifications can be made directly to the polypeptide, such as bycleavage, addition of a linker molecule, addition of a detectablemoiety, such as biotin, substitution of one amino acid for another andthe like. Modifications also embrace fusion proteins comprising all orpart of the TgAMA-1 polypeptide amino acid sequence.

The amino acid sequence of polypeptides may be of natural or non-naturalorigin, that is, they may comprise a TgAMA-1 polypeptide molecule or maycomprise a modified sequence as long as the amino acid sequence retainsthe antigenic property of TgAMA-1. For example, TgAMa-1 polypeptides inthis context may be fusion proteins of a TgAMA-1 polypeptide andunrelated amino acid sequences, synthetic peptides of amino acidsequences shown in SEQ ID NO: 1, peptides isolated from cultured cellsthat express TgAMA-1, and peptides coupled to nonpeptide molecules (forexample in certain drug delivery systems, e.g., across a cell membrane,or detectable labels).

An example, although not intended to be limiting, of a method with whichantigenicity of a TgAMA-1 polypeptide can be tested involves in vivotesting in mice. One test involves the ability to enhance an antibodyresponse to an antigen component of the TgAMA-1 antigen and/or thedelayed-type hypersensitive (DTH) response, measured by an increase infootpad swelling after inoculation in the footpad of the test animal.These measurements can then be compared to corresponding measurements incontrol animals. Serum samples may be drawn from the mice after thefinal inoculation (for example every one or two weeks afterinoculation). Serum can be analyzed for antibodies against the antigenusing known methods in the art, e.g., using an ELISA. DTH response tothe antigen may be measured after the final inoculation (e.g. within 1-7days). An increase in the serum titer of antibodies recognizing theantigen and or an increase in footpad swelling in the animals receivingthe putative TgAMA-1 antigen as compared to the serum titer of thecontrol animals, indicates that putative TgAMA-1 antigen is an antigenicTgAMA-1 polypeptide of the invention.

If a functional variant involves a change to an amino acid if SEQ IDNO:1, the functional variant of the TgAMA-1 polypeptide may haveconservative amino acid substitutions, i.e., substitutions which retaina property of the original amino acid such as charge, hydrophobicity,conformation, etc. Examples of conservative substitutions of amino acidsinclude substitutions made amongst amino acids within the followinggroups: (a) M, I, L, V; (b) F, Y, W; (c) K, R, H; (d) A, G; (e) S, T;(f) Q, N; and (g) E, D.

Other methods for identifying functional variants of SEQ ID NO:1 relyupon the development of amino acid sequence motifs to which potentialepitopes may be compared. (See, e.g., published PCT application ofStrominger and Wucherpfennig (US/96/03182)). In general, these methodsrely upon the development of amino acid sequence motifs to whichpotential epitopes may be compared. Each motif describes a finite set ofamino acid sequences in which the residues at each (relative) positionmay be (a) restricted to a single residue, (b) allowed to vary amongst arestricted set of residues, or (c) allowed to vary amongst all possibleresidues. For example, a motif might specify that the residue at aTgAMA-1 peptide position may be any one of the residues valine, leucine,isoleucine, methionine, or phenylalanine; that the residue at the secondposition must be histidine; that the residue at the third position maybe any amino acid residue; that the residue at the fourth position maybe any one of the residues valine, leucine, isoleucine, methionine,phenylalanine, tyrosine or tryptophan; and that the residue at the fifthposition must be lysine.

Sequence motifs for the TgAMA-1 polypeptide functional variants can bedeveloped by analysis of the antigenic regions of the TgAMA-1polypeptide disclosed herein. By providing a detailed structuralanalysis of the residues involved in the antigenicity of the TgAMA-1polypeptide disclosed herein, one of ordinary skill in the art isenabled to make predictions of sequence motifs for antigenic regions ofthe TgAMA-1 polypeptides.

Using these sequence motifs as search, evaluation, or design criteria,one of ordinary skill in the art is enabled to identify classes ofpeptides (functional variants of the TgAMA-1 polypeptide disclosedherein) which have a reasonable likelihood of being antigenic and/or towhich binding polypeptides such as antibodies can be produced thatinhibit parasite entry into cells. These peptides can be synthesized andtested for activity as described herein. Use of these motifs, as opposedto pure sequence homology (which excludes many peptides which areantigenically similar but quite distinct in sequence) or sequencehomology with unlimited “conservative” substitutions (which admits manypeptides which differ at critical highly conserved sites), represents amethod by which one of ordinary skill in the art can evaluate peptidesfor potential application in the treatment of disease such as toxoplasmainfection.

The ability of the variant TgAMA-1 polypeptides to inhibit toxoplasmaparasite entry into cells, is determined according to standardprocedures. For example, the variant polypeptide can be contacted withthe parasite, and standard procedures may be used to determine whetherthe parasite is inhibited in its ability to enter cells.

Variant TgAMA-1 polypeptides include “fragments” of the polypeptidehaving SEQ ID NO:1. As used herein, a fragment has one or more aminoacids fewer than the polypeptide set forth as SEQ ID NO:1. Those ofordinary skill in the art may apply no more than routine procedures toidentify such fragments, in view of the disclosures provided herein.

Variants and fragments as well as TgAMA-1 binding peptides such asantibodies may be tested for their ability to inhibit Toxoplasmaactivity. One method for inhibiting activity is by inhibiting entry oftoxoplasma into cells. The ability to inhibit entry of toxoplasmaparasite into cells with a TgAMA-1 polypeptide or binding polypeptidecan be assessed using routine screening assays, e.g. by determining thelevel of TgAMA-1 mediated entry of Toxoplasma parasite into cells withand without the presence of the polypeptide. The ability of a putativeTgAMA-1 polypeptide or binding polypeptide to out-compete toxoplasmaparasite entry into cells can be determined by comparing the binding ofthe parasite TgAMA-1 to the cell in the presence and absence of theputative TgAMA-1 polypeptide or binding polypeptide. By comparingputative TgAMA-1 polypeptides or other binding peptides with the peptideof SEQ ID NO:1, additional polypeptides with increased parasiteinhibiting properties can be identified.

Nucleic acid sequences that code for a TgAMA-1 polypeptide or bindingpolypeptides, including allelic variants, are also a part of theinvention. As used herein, an “isolated TgAMA-1 nucleic acid molecule”is a nucleic acid molecule that encodes an antigenic TgAMA-1polypeptide. A TgAMA-1 nucleic acid molecule can be the nucleic acidmolecule set forth as SEQ ID NO:2 or can be a fragment thereof. TheTgAMA-1 nucleic acid molecules of the invention can also be variants ofthe nucleotide sequence set forth as SEQ ID NO:2. The invention alsoencompasses Watson-Crick complements of the foregoing TgAMA-1 nucleicacid molecules. The TgAMA-1 nucleic acids of the invention may encodefragments or variants of the polypeptide set forth as SEQ ID NO:1. Insome embodiments, the TgAMA-1 nucleic acids of the invention do notencode the entire TgAMA-1 polypeptide of SEQ ID NO:1, but do includenucleotide sequences encoding the TgAMA-1 polypeptide fragmentsdisclosed herein, or functional equivalents thereof.

In screening for nucleic acids that encode a TgAMA-1 polypeptide orbinding polypeptide of the invention, nucleic acid hybridization such asa Southern blot or a Northern blot may be performed under highstringency conditions, together with a labeled probe, for example, a ³²Pprobe. The term “high stringency conditions” as used herein refers toparameters with which the art is familiar. Nucleic acid hybridizationparameters may be found in references which compile such methods, e.g.Molecular Cloning: A Laboratory Manual, J. Sambrook, et al., eds.,Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor,N.Y., 1989, or Current Protocols in Molecular Biology, F. M. Ausubel, etal., eds., John Wiley & Sons, Inc., New York. Exemplary high stringencyconditions include hybridization at 65° C. in hybridization buffer(3.5×SSC, 0.02% Ficoll, 0.02% Polyvinyl pyrolidone, 0.02% Bovine SerumAlbumin, 25 mM NaH₂PO₄ (pH7), 0.5% SDS, 2 mM EDTA). SSC is 0.15M SodiumChloride/0.015M Sodium Citrate, pH 7; SDS is Sodium Dodecyl Sulphate;and EDTA is Ethylene diaminetetraacetic acid. After hybridization, themembrane upon which the DNA is transferred can be washed, for example,at 2×SSC at room temperature and then at 0.1-0.5×SSC/0.1×SDS attemperatures up to 68° C. After washing the membrane to which DNAencoding a TgAMA-1 immunogenic polypeptide is finally transferred, themembrane can be placed against X-ray film to detect the radioactivesignal.

There are other conditions, reagents, and so forth that can be used,which result in a similar degree of stringency. The skilled artisan willbe familiar with such conditions, and thus they are not given here. Itwill be understood, however, that the skilled artisan will be able tomanipulate the conditions in a manner to permit the clear identificationof homologs and alleles of nucleic acids encoding the TgAMA-1polypeptide of the invention. The skilled artisan also is familiar withthe methodology for screening cells and libraries for expression of suchmolecules which then are routinely isolated, followed by isolation ofthe pertinent nucleic acid molecule and sequencing.

The invention also includes the use of nucleic acid sequences whichinclude alternative codons that encode the same amino acid residues ofthe TgAMA-1 polypeptide or binding polypeptide of the invention. Forexample, leucine residues can be encoded by the codons CUA, CUC, CUG,CUU, UUA and UUG. Each of the six codons is equivalent for the purposesof encoding a leucine residue. Thus, it will be apparent to one ofordinary skill in the art that any of the leucine-encoding nucleotidetriplets may be employed to direct the protein synthesis apparatus, invitro or in vivo, to incorporate a leucine residue. Similarly,nucleotide sequence triplets which encode other amino acid residuescomprising the TgAMA-1 polypeptide include: GUA, GUC, GUG and GUU(valine codons); GGU, GGA, GGG, GGC (glycine codons); UAC and UAU(tyrosine codons). Other amino acid residues may be encoded similarly bymultiple nucleotide sequences. Thus, the invention embraces degeneratenucleic acids that differ from the native TgAMA-1 polypeptide encodingnucleic acids in codon sequence due to the degeneracy of the geneticcode.

The invention also provides modified nucleic acid molecules, whichinclude additions, substitutions and deletions of one or morenucleotides. In preferred embodiments, these modified nucleic acidmolecules and/or the polypeptides they encode retain at least oneactivity or function of the unmodified nucleic acid molecule and/or thepolypeptides, such as antigenicity, etc. In certain embodiments, themodified nucleic acid molecules encode modified polypeptides, preferablypolypeptides having conservative amino acid substitutions as aredescribed elsewhere herein. The modified nucleic acid molecules arestructurally related to the unmodified nucleic acid molecules and inpreferred embodiments are sufficiently structurally related to theunmodified nucleic acid molecules so that the modified and unmodifiednucleic acid molecules hybridize under stringent conditions known to oneof skill in the art.

For example, modified nucleic acid molecules that encode polypeptideshaving single amino acid changes can be prepared. Each of these nucleicacid molecules can have one, two, or three nucleotide substitutionsexclusive of nucleotide changes corresponding to the degeneracy of thegenetic code as described herein. Likewise, modified nucleic acidmolecules which encode polypeptides having two amino acid changes can beprepared which have, e.g., 2-6 nucleotide changes. Numerous modifiednucleic acid molecules like these will be readily envisioned by one ofskill in the art, including for example, substitutions of nucleotides incodons encoding amino acids 2 and 3, 2 and 4, 2 and 5, 2 and 6, and soon. In the foregoing example, each combination of two amino acids isincluded in the set of modified nucleic acid molecules, as well as allnucleotide substitutions which code for the amino acid substitutions.Additional nucleic acid molecules that encode polypeptides havingadditional substitutions (i.e., 3 or more), additions or deletions(e.g., by introduction of a stop codon or a splice site(s)) also can beprepared and are embraced by the invention as readily envisioned by oneof ordinary skill in the art. Any of the foregoing nucleic acids orpolypeptides can be tested by routine experimentation for retention ofstructural relation or activity to the nucleic acids and/or polypeptidesdisclosed herein.

It will also be understood that the invention embraces the use of thesequences in expression vectors, as well as to transfect host cells andcell lines. A host cell, as used herein, is any cell capable ofexpressing a peptide in the presence of appropriate expression vectors.Host cells include but are not limited to prokaryotic (e.g., E. coli),or eukaryotic (e.g., CHO cells, COS cells, yeast expression systems andrecombinant baculovirus expression in insect cells, plasmids in HighFive™ Cells). Especially useful are insect cells as host cells forexpression in the invention. An example of useful insect cells, althoughnot intended to be limiting, are High Five™ insect cells (see Examples).Plants may also be used to express the TgAMA-1 vaccines of theinvention. The expression vectors require that the pertinent sequence,i.e., those described supra, be operably linked to a promoter. Thus, thepolypeptides of the invention may be produced in host cells anddelivered to a subject.

Alternatively, the peptides may be produced in vivo followingadministration of an expression vector with the TgAMA-1 nucleic acid toa subject. Delivery of expression vectors encoding the TgAMA-1 sequencesin vivo and/or in vitro can be via the use of nucleic acid deliverysystems known in the art (see, e.g., Allsopp et al., Eur. J Immunol.26(8):1951-1959, 1996). Recombinant vectors including viruses selectedfrom the group consisting of adenoviruses, adeno-associated viruses,poxviruses including vaccinia viruses and attenuated poxviruses such asNYVAC, Semliki Forest virus, Venezuelan equine encephalitis virus,retroviruses, Sindbis virus, and Ty virus-like particle, plasmids (e.g.“naked” DNA), bacteria (e.g. the bacterium Bacille Calmette Guerin,BCG), and the like can be used in such delivery. For example, theexpression vectors can be administered in vivo to produce the antigen asa vaccine. Other viruses, expression vectors and the like which areuseful in preparation of a vaccine antigen in vivo are known to one ofordinary skill in the art. Since nucleic acids have some adjuvantproperties an antigen expressed in vivo from an expression vector maynot require an additional adjuvant. One can test the TgAMA-1 moleculedelivery systems in standard model systems such as mice to determineefficacy of the delivery system. The systems also can be tested in humanclinical trials.

As used herein, a “vector” may be any of a number of nucleic acids intowhich a desired sequence may be inserted by restriction and ligation fortransport between different genetic environments or for expression in ahost cell. Vectors are typically composed of DNA although RNA vectorsare also available. Vectors include, but are not limited to, plasmids,phagemids, bacteria and virus genomes as disclosed herein, such asadenovirus, poxvirus and BCG. A cloning vector is one which is able toreplicate in a host cell, and which is further characterized by one ormore endonuclease restriction sites at which the vector may be cut in adeterminable fashion and into which a desired DNA sequence may beligated such that the new recombinant vector retains its ability toreplicate in the host cell. In the case of plasmids, replication of thedesired sequence may occur many times as the plasmid increases in copynumber within the host bacterium or just a single time per host beforethe host reproduces by mitosis. In the case of phage, replication mayoccur actively during a lytic phase or passively during a lysogenicphase. An expression vector is one into which a desired DNA sequence maybe inserted by restriction and ligation such that it is operably joinedto regulatory sequences and may be expressed as an RNA transcript.Vectors may further contain one or more marker sequences suitable foruse in the identification of cells which have or have not beentransformed or transfected with the vector. Markers include, forexample, genes encoding proteins which increase or decrease eitherresistance or sensitivity to antibiotics or other compounds, genes whichencode enzymes whose activities are detectable by standard assays knownin the art (e.g., β-galactosidase, luciferase or alkaline phosphatase),and genes which visibly affect the phenotype of transformed ortransfected cells, hosts, colonies or plaques (e.g., green fluorescentprotein). Preferred vectors are those capable of autonomous replicationand expression of the structural gene products present in the DNAsegments to which they are operably joined.

As used herein, a coding sequence and regulatory sequences are said tobe “operably” joined when they are covalently linked in such a way as toplace the expression or transcription of the coding sequence under theinfluence or control of the regulatory sequences. If it is desired thatthe coding sequences be translated into a functional protein, two DNAsequences are said to be operably joined if induction of a promoter inthe 5′ regulatory sequences results in the transcription of the codingsequence and if the nature of the linkage between the two DNA sequencesdoes not (1) result in the introduction of a frame-shift mutation, (2)interfere with the ability of the promoter region to direct thetranscription of the coding sequences, or (3) interfere with the abilityof the corresponding RNA transcript to be translated into a protein.Thus, a promoter region would be operably joined to a coding sequence ifthe promoter region were capable of effecting transcription of that DNAsequence such that the resulting transcript might be translated into thedesired protein or polypeptide. As noted above, some nucleic acidsexpress only fragments of TgAMA-1 polypeptides that include antigenicfragments.

The precise nature of the regulatory sequences needed for geneexpression may vary between species or cell types, but shall in generalinclude, as necessary, 5′ non-transcribed and 5′ non-translatedsequences involved with the initiation of transcription and translationrespectively, such as a TATA box, capping sequence, CAAT sequence, andthe like. Especially, such 5′ non-transcribed regulatory sequences willinclude a promoter region which includes a promoter sequence fortranscriptional control of the operably joined gene. Regulatorysequences may also include enhancer sequences or upstream activatorsequences as desired. The vectors of the invention may optionallyinclude 5′ leader or signal sequences. The choice and design of anappropriate vector is within the ability and discretion of one ofordinary skill in the art.

Expression vectors containing all the necessary elements for expressionare commercially available and known to those skilled in the art. See,e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, SecondEdition, Cold Spring Harbor Laboratory Press, 1989. Cells aregenetically engineered by the introduction into the cells ofheterologous DNA (RNA) encoding a TgAMA-1 polypeptide of the invention.That heterologous DNA (RNA) is placed under operable control oftranscriptional elements to permit the expression of the heterologousDNA in the host cell.

Preferred systems for mRNA expression in mammalian cells are those suchas pcDNA3.1 (available from Invitrogen, Carlsbad, Calif.) that contain aselectable marker such as a gene that confers G418 resistance (whichfacilitates the selection of stably transfected cell lines) and thehuman cytomegalovirus (CMV) enhancer-promoter sequences. Additionally,suitable for expression in primate or canine cell lines is the pCEP4vector (Invitrogen), which contains an Epstein Barr virus (EBV) originof replication, facilitating the maintenance of plasmid as a multicopyextrachromosomal element. Another expression vector is the pEF-BOSplasmid containing the promoter of polypeptide Elongation Factor 1α,which stimulates efficiently transcription in vitro. The plasmid isdescribed by Mishizuma and Nagata (Nuc. Acids Res. 18:5322, 1990), andits use in transfection experiments is disclosed by, for example,Demoulin (Mol. Cell. Biol. 16:4710-4716, 1996). Still another preferredexpression vector is an adenovirus, described by Stratford-Perricaudet,which is defective for E1 and E3 proteins (J. Clin. Invest. 90:626-630,1992). The use of the adenovirus to express proteins for immunization isdisclosed by Wamier et al., in intradermal injection in mice forimmunization against P1A (Int. J Cancer, 67:303-310, 1996).

The invention also embraces expression kits, which allow the artisan toprepare a desired expression vector or vectors. Such expression kitsinclude at least separate portions of at least two of the previouslydiscussed materials. Other components may be added, as desired.

In another aspect of the invention transgenic non-human animalscomprising the expression vector of the invention are provided. Suchtransgenic animals are capable of expressing a variable level of TgAMA-1polypeptide. In some embodiments, a mammal is genetically modified toproduce TgAMA-1 in its milk Techniques for performing such geneticmodifications are described in U.S. Pat. No. 6,013,857, issued Jan. 11,2000 for :Transgenic Bovines and Milk from Transgenic Bovines.” Thegenome of the transgenic animal is modified to comprise a transgenecomprising a DNA sequence encoding TgAMA-1 operably linked to a mammarygland promoter. Expression of the DNA sequence results in the productionof TgAMA-1 in the milk. TgAMA-1 may then be isolated from milk obtainedfrom the transgenic mammal (e.g. using a column comprising an antibodywhich binds to TgAMA-1). The transgenic mammal is preferably a bovinespecies.

The invention also encompasses peptides that bind to TgAMA-1, refereedto herein as TgAMA-1 polypeptides or peptides. TgAMA-1 bindingpolypeptides include but are not limited to anti-TgAMA-1 antibodiesincluding polyclonal and monoclonal antibodies, antibody fragments, andother non-antibody peptides. Antibodies useful in the methods of theinvention include but are not limited to monoclonal antibody B3.90,which binds to TgAMA-1 and is described herein, and polyclonalantibodies such as UVT59, which is described herein.

The TgAMA-1 binding polypeptides (e.g. anti-TgAMA-1 antibodies) of theinvention selectively bind to TgAMA-1 polypeptides and in someembodiments inhibit entry of Toxoplasma gondii or other toxoplasmaparasite into cells. Such TgAMA-1 binding polypeptides are prepared bystandard methods.

In view of the foregoing, the invention also permits the artisan totreat a subject having a toxoplasma infection or at risk of developing atoxoplasma infection. Treatments include administering TgAMA-1polypeptides, optionally in the form of a vaccine or a TgAMA-1 bindingpolypeptide, including the anti-TgAMA-1 antibodies of the inventiondisclosed herein.

In certain embodiments, the TgAMA-1 polypeptides and anti-TgAMA-1antibodies of the invention are used to produce antibodies(“anti-TgAMA-1 antibodies”) using standard techniques well known to theart. Standard reference works setting forth the general principles ofantibody production include Catty, D., Antibodies, A Practical Approach,Vol. 1, IRL Press, Washington D.C. (1988); Klein, J., Immunology: TheScience of Cell-Non-Cell Discrimination, John Wiley and Sons, New York(1982); Kennett, R., et al., Monoclonal Antibodies Hybridoma, A NewDimension In Biological Analyses, Plenum Press, New York (1980);Campbell, A., Monoclonal Antibody Technology, in Laboratory Techniquesand Biochemistry and Molecular Biology, Vol. 13 (Burdon, R. et al.EDS.), Elsevier Amsterdam (1984); and Eisen, H. N., Microbiology, thirdedition, Davis, B. D. et al. EDS. (Harper & Rowe, Philadelphia (1980).See also, U.S. Pat. No. 5,101,017, issued Mar. 31, 1992 to Rubinstein,et al., entitled, “Antibodies for providing protein against P. vivaxmalaria infection,” which also reports the preparation of anti-idiotypicantibodies for treating infectious disease. References that reportvaccine approaches for treating malaria disease, which is also aparasitic infection, include: U.S. Pat. No. 6,066,623, issued toHoffinan, et al., entitled “Polynucleotide vaccine protective againstmalaria, methods of protection and vector for delivering polynucleotidevaccines”; and U.S. Pat. No. 6,120,770, issued to Adams et al., entitled“Plasmodium proteins useful for preparing vaccine compositions.”

The antibodies of the present invention are prepared using any of avariety of methods, including administering the TgAMA-1 polypeptides ofthe invention, antibodies selective for the foregoing, and the like toan animal to induce monoclonal or polyclonal antibodies. The productionof monoclonal antibodies is according to techniques well known in theart.

Non-limiting examples of supports for affinity-separation of antibodies,including monoclonals, include the following: activated Sepharose,activated cellulose and activated Sephadex. “Activated” refers to thecreation, on the insoluble material, of reactive chemical groups thatwill form covalent linkages with the antibody molecules when incubatedtogether under appropriate conditions. Typically, reactive groups areintroduced into the insoluble substrate by the action of cyanogenbromide (CNBr) at high pH.

Significantly, as is well-known in the art, only a small portion of anantibody molecule, the paratope, is involved in the binding of theantibody to its epitope (see, in general, Clark, W. R. (1986) TheExperimental Foundations of Modem Immunology Wiley & Sons, Inc., NewYork; Roitt, I. (1991) Essential Immunology, 7th Ed., BlackwellScientific Publications, Oxford). The pFc′ and Fc regions, for example,are effectors of the complement cascade but are not involved in antigenbinding. An antibody from which the pFc′ region has been enzymaticallycleaved, or which has been produced without the pFc′ region, designatedan F(ab′)₂ fragment, retains both of the antigen binding sites of anintact antibody. Similarly, an antibody from which the Fc region hasbeen enzymatically cleaved, or which has been produced without the Fcregion, designated an Fab fragment, retains one of the antigen bindingsites of an intact antibody molecule. Fab fragments consist of acovalently bound antibody light chain and a portion of the antibodyheavy chain denoted Fd. The Fd fragments are the major determinant ofantibody specificity (a single Fd fragment may be associated with up toten different light chains without altering antibody specificity) and Fdfragments retain epitope-binding ability in isolation.

Within the antigen-binding portion of an antibody, there arecomplementary determining regions (CDRs), which directly interact withthe epitope of the antigen, and framework regions (FRs), which maintainthe tertiary structure of the paratope (see, in general, Clark, 1986;Roitt, 1991). In both the heavy chain Fd fragment and the light chain ofIgG immunoglobulins, there are four framework regions (FR1 through FR4)separated respectively by three complementarity determining regions(CDR1 through CDR3). The CDRs, and in particular the CDR3 regions, andmore particularly the heavy chain CDR3, are largely responsible forantibody specificity.

It is now well established in the art that the non-CDR regions of amammalian antibody may be replaced with similar regions of conspecificor heterospecific antibodies while retaining the epitopic specificity ofthe original antibody. This is most clearly manifested in thedevelopment and use of “humanized” antibodies in which non-human CDRsare covalently joined to human FR and/or Fc/pFc′ regions to produce afunctional antibody. See, e.g., U.S. Pat. Nos. 4,816,567, 5,225,539,5,585,089, 5,693,762 and 5,859,205. Accordingly, humanized anti-TgAMA-1antibodies, particularly those that selectively bind to SEQ ID NO:1, andthe use of such antibodies (e.g., to provide passive immunity to asubject) are embraced with the inventions disclosed herein.

For example, PCT International Publication Number WO92/04381 teaches theproduction and use of humanized murine RSV antibodies in which at leasta portion of the murine FR regions have been replaced by FR regions ofhuman origin. Such antibodies, including fragments of intact antibodieswith antigen-binding ability, are often referred to as “chimeric”antibodies.

Thus, the present invention also provides for F(ab′)₂, Fab, Fv and Fdfragments; chimeric antibodies in which the Fc and/or FR and/or CDR1and/or CDR2 and/or light chain CDR3 regions have been replaced byhomologous human or non-human sequences; chimeric F(ab′)₂ fragmentantibodies in which the FR and/or CDR1 and/or CDR2 and/or light chainCDR3 regions have been replaced by homologous human or non-humansequences; chimeric Fab fragment antibodies in which the FR and/or CDR1and/or CDR2 and/or light chain CDR3 regions have been replaced byhomologous human or non-human sequences; and

chimeric Fd fragment antibodies in which the FR and/or CDR1 and/or CDR2regions have been replaced by homologous human or non-human sequences.The present invention also includes so-called single chain antibodiesand human monoclonal antibodies, such as those produced by mice havingfunctional TgAMA-1 loci.

Such antibodies also may be used to identify tissues expressing proteinor to purify protein. Antibodies, also may be coupled to specificlabeling agents for imaging or to anti-infectious agents, toxins such asricin, other cytostatic or cytolytic drugs, and so forth, fortherapeutic purposes.

The invention also involves the use of anti-idiotypic antibodies. Byusing monoclonal antibodies that interact with TgAMA-1 polypeptide, itis also possible to produce anti-idiotypic antibodies which can be usedto screen other molecules to identify whether the other molecule has thesame binding specificity as the monoclonal antibody. Such anti-idiotypicantibodies can be produced using well-known hybridoma techniques (Kohlerand Milstein, Nature, 256:495, 1975). An anti-idiotypic antibody is anantibody which recognizes unique determinants present on the knownmonoclonal antibodies. These determinants are located in thehypervariable region of the antibody. It is this region which binds to agiven epitope and, thus, is responsible for the specificity of theantibody. An anti-idiotypic antibody can be prepared by immunizing ananimal with a monoclonal antibody. The immunized animal will recognizeand respond to the idiotypic determinants of the immunizing monoclonalantibodies and produce an antibody to these idiotypic determinants. Byusing the anti-idiotypic antibodies of the immunized animal, which arespecific for the monoclonal antibodies of the invention, it is possibleto identify other clones with the same idiotype as the monoclonalantibody used for immunization. Idiotypic identity between monoclonalantibodies of two cell lines demonstrates that the two monoclonalantibodies are the same with respect to their recognition of the sameepitopic determinant. Thus, by using anti-idiotypic antibodies, it ispossible to identify other hybridomas expressing monoclonal antibodieshaving the same epitopic specificity.

It is also possible to use the anti-idiotype technology to producemonoclonal antibodies which mimic an epitope. For example, ananti-idiotypic monoclonal antibody made to a first monoclonal antibodywill have a binding domain in the hypervariable region which is theimage of the epitope bound by the first monoclonal antibody.

When administered, the therapeutic compositions of the present inventionare administered in pharmaceutically acceptable preparations. Suchpreparations may routinely contain pharmaceutically acceptableconcentrations of salt, buffering agents, preservatives, compatiblecarriers, supplementary immune potentiating agents such as adjuvants andcytokines and optionally other therapeutic agents.

The term “pharmaceutically acceptable” means a non-toxic material thatdoes not interfere with the effectiveness of the biological activity ofthe active ingredients. The characteristics of the carrier will dependon the route of administration.

The therapeutics of the invention can be administered by anyconventional route, including injection or by gradual infusion overtime. The administration may, for example, be oral, intravenous,intraperitoneal, intramuscular, intranasal, intracavity, subcutaneous,intradermal, or transdermal.

Preparations for parenteral administration include sterile aqueous ornon-aqueous solutions, suspensions, and emulsions. Examples ofnon-aqueous solvents are propylene glycol, polyethylene glycol,vegetable oils such as olive oil, and injectable organic esters such asethyl oleate. Aqueous carriers include water, alcoholic/aqueoussolutions, emulsions or suspensions, including saline and bufferedmedia. Parenteral vehicles include sodium chloride solution, Ringer'sdextrose, dextrose and sodium chloride, lactated Ringer's or fixed oils.Intravenous vehicles include fluid and nutrient replenishers,electrolyte replenishers (such as those based on Ringer's dextrose), andthe like. Preservatives and other additives may also be present such as,for example, antimicrobials, anti-oxidants, chelating agents, and inertgases and the like.

The invention involves the use of various materials disclosed herein to“immunize” subjects or as “vaccines.” A “vaccine’ as used herein is anantigen in a pharmaceutical formulation and optionally includes anadjuvant. As used herein, “immunization” or “vaccination” meansincreasing or activating an immune response against an antigen. It doesnot require elimination or eradication of a condition but rathercontemplates the clinically favorable enhancement of an immune responsetoward an antigen. Generally accepted animal models can be used fortesting of immunization against toxoplasma using a toxoplasma antigenpolypeptide or nucleic acid. For example, toxoplasma parasite can beintroduced into a mouse to create the disease, and one or moretoxoplasma antigen can be delivered by the methods described herein. Theeffect on the toxoplasma disorder can be assessed as a measure of theeffectiveness of the toxoplasma antigen immunization. Of course, testingof the foregoing animal model using more conventional methods forimmunization include the administration of one or more toxoplasmaantigen polypeptides or peptides derived therefrom, optionally combinedwith one or more adjuvants and/or cytokines to boost the immuneresponse. Methods for immunization, including formulation of a vaccinecomposition and selection of doses, route of administration and theschedule of administration (e.g. primary and one or more booster doses),are well known in the art. The tests also can be performed in humans,where the end point is to test for the presence of enhanced levels ofcirculating CTLs against cells bearing the antigen, to test for levelsof circulating antibodies against the antigen, to test for the presenceof cells expressing the antigen and so forth.

As part of the immunization compositions, one or more TgAMA-1polypeptides are administered optionally with one or more adjuvants toinduce an immune response or to increase an immune response. An adjuvantis a substance incorporated into or administered with antigen whichpotentiates the immune response. Adjuvants may include, but are notlimited to: mineral gels, e.g., aluminum hydroxide; surface activesubstances such as lysolecithin, pluronic polyols; polyanions; peptides;alum, MDP, N-acetyl-muramyl-L-threonyl-D-isoglutamine (thr-MDP),N-acetyl-nor-muramyl-L-analyl-D-isoglutamine, andN-acetylmuramyl-L-alanyl-D-isoglutaminyl-L-analanine-2-(1′-2′dipalmitoyl-sn-glycero-3-hydroxyphosphroyloxy)-ethylamine,monophosphoryl lipid A; saponins (QS21; DQS21); QS-7, QS-17, QS-18, andQS-L1; incomplete Freund's adjuvant; complete Freund's adjuvant;montanide; vitamin E, oil emulsions, and various water-in-oil emulsionsprepared from biodegradable oils such as squalene and/or tocopherol.

Adjuvants may enhance the immunological response by providing areservoir of antigen (extracellularly or within macrophages), activatingmacrophages and stimulating specific sets of lymphocytes. Adjuvants ofmany kinds are well known in the art.

In some embodiments, the polypeptides are administered mixed with acombination of DQS21I/MPL. The ratio of DQS21 to MPL typically will beabout 1:10 to 10:1, preferably about 1:5 to 5:1 and more preferablyabout 1:1. Typically for human administration, DQS21 and MPL will bepresent in a vaccine formulation in the range of about 1 μg to about 100μg. Other adjuvants are known in the art and can be used in theinvention (see, e.g. Goding, Monoclonal Antibodies: Principles andPractice, 2nd Ed., 1986). Methods for the preparation of mixtures oremulsions of peptide and adjuvant are well known to those of skill inthe art of vaccination.

Other agents which stimulate the immune response of the subject can alsobe administered to the subject. For example, other cytokines are alsouseful in vaccination protocols as a result of their lymphocyteregulatory properties. Many other cytokines useful for such purposeswill be known to one of ordinary skill in the art, includinginterleukin-12 (IL-1 2) which has been shown to enhance the protectiveeffects of vaccines (see, e.g., Science 268: 1432-1434, 1995), GM-CSFand IL-18. Thus cytokines can be administered in conjunction withantigens and adjuvants to increase the immune response to the antigens.

In some embodiments of the invention, the vaccine is a proteosomevaccine. Proteosomes are useful for immunopotentiation by renderingpeptides immunogenic and enhancing the immunostimulating properties oflarger peptides, proteins, and protein fragments. Methods for preparingproteosomes include, but are not limited to, preparation frommeningococci, as described in U.S. Pat. No. 5,726,292, the contents ofwhich is hereby incorporated in its entirety.

The preparations of the invention are administered in effective amounts.An effective amount is that amount of a pharmaceutical preparation thatalone, or together with further doses, stimulates the desired response.In the case of treating an infectious disease such as toxoplasma, thedesired response is inhibiting the onset, stage or progression of thedisease or infection. This may involve only slowing the progression ofthe disease temporarily, although more preferably, it involves haltingthe progression of the disease permanently, or preventing infection.

The TgAMA-1 molecule dosage may be adjusted by the individual physicianor veterinarian, particularly in the event of any complication. Atherapeutically effective amount typically varies from 0.01 mg/kg toabout 1000 mg/kg, preferably from about 0.1 mg/kg to about 200 mg/kg,and most preferably from about 0.2 mg/kg to about 20 mg/kg, in one ormore dose administrations daily, for one or more days.

The absolute amount will depend upon a variety of factors, including thematerial selected for administration, whether the administration is insingle or multiple doses, and individual patient parameters includingage, physical condition, size, weight, and the stage of the disease.These factors are well known to those of ordinary skill in the art andcan be addressed with no more than routine experimentation.

In one embodiment, the therapeutically effective amount of the TgAMA-1molecule is that amount effective to inhibit toxoplasma entry intocells. Such inhibition can be determined using standard assays asdescribed above. In other embodiments a therapeutically effective amountis that amount effective to induce an immune response against theparasite. Measurements of acute toxoplasma infection, includingisolation of the parasite from either blood or other body fluids aftersubinoculation of the body fluid into the peritoneal cavity of mice canbe used to assess the levels of parasites remaining in the blood afterexposure. (see Harrison's Principles of Internal Medicine, 14/e, McGrawHill Companies, New York, 1998). If no parasites are found in themouse's peritoneal fluid, its anti-Toxoplasma serum titer can beevaluated 4 to 6 weeks after inoculation. The presence of Toxoplasmagondii in a subject's body fluid represents an acute infection, and thepresence of Toxoplasma gondii in tissue biopsies is an indication onlyof the presence of tissue cysts and not acute toxoplasmosis. (seeHarrison's Principles of Internal Medicine, 14/e, McGraw Hill Companies,New York, 1998). Additional methods of diagnosis and assessment ofchronic and acute toxoplasma infection are known to those of skill inthe art.

In addition, diagnosis of an acute Toxoplasma gondii infection bydetection of the simultaneous presence of IgG and IgM antibody toToxoplasma in the subject's serum. The presence of circulating IgAsuggests an acute infection. The Sabin-Feldman dye test, the indirectfluorescent antibody test, and the enzyme-linked immunosorbent assay(ELISA) all satisfactorily measure circulating IgG antibody toToxoplasma. Positive IgG titers (>1:10) can be detected as early as 2 to3 weeks after infection. These titers usually peak at 6 to 8 weeks anddecline slowly to a new baseline level that persists for life. Themethods currently available for this determination are thedouble-sandwich IgM-ELISA and the IgM-immunosorbent assay (IgM-ISAGA).The double-sandwich IgA-ELISA is more sensitive than the IgM-ELISA fordetecting congenital infection in the fetus and newborn. (see Harrison'sPrinciples of Internal Medicine, 14/e, McGraw Hill Companies, New York,1998).

In addition to the diagnostic tests described above, clinical featuresof toxoplasma infection can be monitored for assessment of infection.Theses features include, but are not limited to: assessment of thepresence of eye lesions, brain lesions, and brain inflammation. Suchassessment can be with methods known to one of ordinary skill in theart, such as ophthalmologic testing, CSF evaluation, and radiologicstudies. (see Harrison's Principles of Internal Medicine, 14/e, McGrawHill Companies, New York, 1998).

These types of tests, as well as others known to those of ordinary skillin the medical arts, may be used to assess the toxoplasma infectionstatus of a subject and to evaluate a therapeutically effective amountof TgAMA-1 molecule or TgAMA-1 binding polypeptides administered. Afirst determination of toxoplasma infection may be obtained using one ofthe methods described above, and a subsequent determination of infectioncan be done and a comparison of the infection levels may be used toassess the effectiveness of TgAMA-1 molecule or TgAMA-1 bindingpolypeptides administration as a prophylactic or a treatment of thetoxoplasma infection. Absence of a toxoplasma infection may be anindication for prophylactic intervention by administering TgAMA-1molecules or TgAMA-1 binding polypeptides to prevent toxoplasmainfection.

The TgAMA-1 molecules and TgAMA-1 binding polypeptides may beadministered alone, in combination with each other, and/or incombination with other anti-toxoplasma drug therapies. Antitoxoplasmaagents (for treatment and/or prophylaxis) that may be administered withTgAMA-1 molecules or TgAMA-1 binding polypeptides may include, but arenot limited to: pyrimethamine plus either sulfadiazine or clindamycin;trimethoprim; protein synthesis inhibitors such as clindamycin,chlortetracycline, and azithromycin;. purine synthesis inhibitors suchas arprinocid; atovaquone; spiramycin plus prednisone; Dapsone(diaminodiphenyl sulfone); macrolides including roxithromycin,clarithromycin, and azithromycin; and phenytoin.

The above-described drug therapies are well known to those of ordinaryskill in the art and are administered by modes known to those of skillin the art. The drug therapies are administered in amounts that areeffective to achieve the physiological goals (to reduce toxoplasmainfection, and/or reduce toxoplasma titer in a subject), in combinationwith the TgAMA-1 molecules of the invention. Thus, it is contemplatedthat the drug therapies may be administered in amounts which are notcapable of preventing or reducing the physiological consequences of thetoxoplasma infections when the drug therapies are administered alone,but which are capable of preventing or reducing the physiologicalconsequences of toxoplasma infection when administered in combinationwith the TgAMA-1 molecules of the invention.

The vaccine formulations of the invention may be administered to conferimmunity to a subject at risk of exposure to toxoplasma, which therebyprevents, reduces the severity of or delays the onset of a subsequentToxoplasma infection. Alternatively, the vaccines may be administeredduring an ongoing Toxoplasma infection to improve the effectiveness ofthe host's response to the infections Toxoplasma organism.

The invention also provides a pharmaceutical kit comprising one or morecontainers comprising one or more of the TgAMA-1 molecules and/orantibodies of the invention and or formulations of the invention. Thekit may also include instructions for the use of the one or more TgAMA-1molecules and/or antibodies of the invention for the treatment oftoxoplasma infection.

EXAMPLES Example 1 Antibody Generation and Characterization of TgAMA-1

Procedure

Parasite Culture

T. gondii tachyzoites (RH strain, unless otherwise indicated) werecultured in human foreskin fibroblasts as previously described [5] andfiltered through a 10 μm polycarbonate filter (Poretics, LivermoreCalif.) prior to use.

Antibodies

MAbs: MAb B3.90 (against TgAMA-1) and A3.2 (against GRA8) were generatedas described [3, 6] and purified by ion exchange and gel filtrationchromatography [7]. Ascites fluid containing MAb 6D10 (against MIC2) wasprepared as described [1]. Ascites fluid containing MAb Tg49 (againstROP1) was generously provided by Joseph Schwartzman (Dartmouth College,Hanover N.H.). MAb 40-1a (against E. coli β-galactosidase) was developedby J. R. Sanes and obtained from the Developmental Studies HybridomaBank (University of Iowa, Department of Biological Sciences, Iowa CityIowa) as a hybridoma supernatant.

Polyclonal antibody UVT59: A synthetic peptide corresponding to residues496-515 of TgAMA-1 (acetyl-EFQSDRGARKKRPSDLMQEAC-amide (SEQ ID NO:3))was coupled to keyhole limpet hemocyanin using the Imject MaleimideActivated mcKLH Kit (Pierce, Rockford Ill.). The peptide-carrierconjugate was used to generate rabbit polyclonal antisera (CocalicoBiologicals Inc., Reamstown Pa.); serum titers were determined bywestern blot and immunofluorescence microscopy. Synthetic peptidecoupled to agarose using the SulfoLink Kit (Pierce) was used to affinitypurify AMA-I-specific antibody UVT59 from total serum as recommended bythe manufacturer, except that 0.01 vol of stock protease inhibitors(aqueous stock contains 2 mg/ml aprotinin, 2 mg/ml leupeptin, 16 mg/mlbenzamidine, and 5 mg/ml 4-(2-aminoethyl)-phenylsulfonylfluoride; DMSOstock contains 5 mg/ml pepstatin) were added to the serum beforeapplying it to the peptide column.

Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) andWestern Blotting

Proteins were resolved by SDS-PAGE in the presence (reducing) or absence(non-reducing) of 5% (v/v) β-mercaptoethanol and western blotted asdescribed[3], using MAb B3.90, MAb 6D10, MAb 40-1a and polyclonal serumUVT 59 at dilutions of 23.2 μg/ml, 1/5000 (v/v), 1/100 (v/v), and1/10,000 (v/v), respectively. Where indicated, blots were stripped bysequential incubation in PBS (2 changes, 5 min each), 4% (w/v)trichloroacetic acid (2 changes, 10 min each), and PBS (2 changes, 5 mineach). Stripped blots were either reblocked and probed with a differentantibody or exposed directly to X-ray film.

Triton X-114 (TX-114) Phase Partitioning

TX-114 phase partitioning of total parasite extracts was carried out aspreviously described [6]. After partitioning, the detergent phase wasdiluted to the original extract volume (4×10⁷ parasite equivalents/ml)with 50 mM Tris-HCl, pH 7.4 and 100 mM NaCl, supplemented with 3.0 U/mlBacillus cereus phosphatidylinositol-specific phospholipase C (PI-PLC;Molecular Probes, Eugene Oreg.) and sequentially incubated for 5 min onice, 35 min at 37° C. and 5 min on ice. The PI-PLC-treated detergentphase was then subjected to 2 additional rounds of phase partitioning,and analyzed by SDS-PAGE/western blotting.

Immunoaffinity Purification and Sequence Analysis

MAb B3.90 was covalently cross-linked to Affi-Gel Protein A-conjugatedagarose (BioRad, Hercules Calif.) as previously described [8].Approximately 2.5 mg of IgG was coupled per 1 ml of resin. Parasiteswere washed twice in phosphate-buffered saline (PBS), pH 7.4 andextracted for 45 min on ice in EXTR buffer (0.5% [v/v] Triton X-100(TX-100), 50 mM Tris, pH 7.4, 100 mM NaCl) supplemented with 0.01volumes of the aqueous and DMSO protease inhibitor stocks. The extractswere centrifuged at 14,000×g for 5 min at 4° C. to remove insolublematerial; the protein concentration of the supernatant was determinedusing the DC Protein Assay (BioRad). Extract (5 ml, 3.5 mg totalprotein) was added to 450 μL of antibody-conjugated beads (prewashedthree times with EXTR buffer) and rotated gently for 2 h at 4° C.,followed by 4 washes (batchwise) with EXTR buffer. Bound antigen waseluted from the washed beads using two sequential incubations with 400μl of non-reducing SDS-PAGE sample buffer for 10 min at 100° C. Thepooled eluate was concentrated 10-fold using a Centricon RC/YM-30centrifugal filter device (30,000 MWCO; Millipore, Bedford Mass.) andsubjected to SDS-PAGE. The gel was stained for 30 min with 0.1% (w/v)Coomassie R-250 in 50% (v/v) methanol, 10% (v/v) acetic acid anddestained for 1 h in 10% (v/v) methanol and 7.5% (v/v) acetic acid. Thepurified antigen was cut out of the gel, digested with trypsin, andanalyzed at the Harvard Microchemistry Facility (Cambridge Mass.) bymicrocapillary reverse-phase HPLC nano-electrospray tandem massspectrometry (μLC/MS/MS) on a Finnigan LCQ quadropole ion trap massspectrometer. The fragmentation spectra were correlated with knownsequences using previously described algorithms [9, 10].

Immunofluorescence

Methanol fixation. Parasites were attached to the surface of glasscoverslips using Cell Tack (Becton Dickinson, Bedford Mass.) asdescribed [3]. They were washed twice with PBS, pH 7.4, at 4° C. andfixed in 100% methanol for 5 min at −20° C. All subsequent incubationswere carried out at 4° C. The fixed parasites were washed 4 times inPBS, blocked for 10 min in PBS containing 0.5% (w/v) bovine serumalbumin (PBS-BSA), and incubated for 45 min in primary antibody dilutedin PBS-BSA as follows: B3.90, 11.5 μg/ml; A3.2, 0.5 μg/ml; 6D10, 1/50(v/v); Tg49, 1/100 (v/v); affinity purified UVT59, 12.5 μg/ml. They werethen washed 3 times with PBS, incubated for 30 min in PBS-BSA containingeither 1.5 μg/ml Alexa546-conjugated goat anti-mouse IgG (MolecularProbes, Eugene Oreg.) or 0.9 μg/ml Alexa546-conjugated goat anti-rabbitIgG (Molecular Probes), and washed three times with PBS. For dual labelimmunofluorescence, parasites were then incubated for 45 min in PBS-BSAcontaining MAb B3.90 which had been directly conjugated to Alexa488using an Alexa488 Protein Labeling kit (Molecular Probes). The labeledparasites were washed 5 times in PBS and mounted on glass slides forobservation.

Formaldehyde/glutaraldehyde fixation. Samples were processed as above,except that the methanol fixation step was replaced by 30 min at 4° C.in 2.5% (v/v) formaldehyde, 0.025% (v/v) glutaraldehyde. Whereindicated, samples were permeabilized by including 0.1% (v/v) TX-100 inthe PBS-BSA block and in the primary antibody incubation.

Unfixed/unpermeabilized suspension assay. Tachyzoites were washed twicein PBS, pH 7.4 by centrifugation for 4 min at 1000×g (23° C) andincubated for 10 min at 4° C. in PBS-BSA, followed by 1 hr at 4° C. inPBS-BSA containing primary antibody, diluted as above. The labeled cellswere washed 3 times in PBS, post-fixed 25 min at 4° C. in PBS containing2.5% (v/v) formaldehyde and 0.025% (v/v) glutaraldehyde, washed 3 timesin PBS, incubated with fluorescently conjugated secondary antibody asabove, washed 5 times in PBS and mounted on glass slides in PBS forobservation.

Microscopy. Samples were observed on a Nikon Eclipse E400 fluorescencemicroscope using Nikon filter cube XF100 (excitation 455-495 nm,emission 515-560 nm) for Alexa488 and filter cube XF102 (excitation535-590 nm, emission 605-710 nm) for Alexa546. No Alexa488 fluorescencewas detectable using the XF102 filter, and no Alexa546 fluorescence wasdetectable using the XF100 filter. Digitized images were obtained usingeither a VE1000SIT camera (Dage-MTI, Michigan City Ind.) with an LG-3framegrabber and Scion Image v 1.6 software (Scion Corp., Frederick Md.)or a SpotRT monochrome camera driven by Spot v.3.01 (AppleEvent)software (Diagnostic Instruments Inc., Sterling Heights Mich.).

Immunoelectron Microscopy

Cryoimmunoelectron microscopy was performed as previously described [6],using MAb B3.90 (25 ug/ml) as primary antibody. No immunogold labelingwas observed when primary antibody was omitted.

Secretion Assays

Tachyzoites (2F strain, constitutively expressing cytoplasmicβ-galactosidase [generous gift of David Sibley]) were washed twice inDMEM+20 mM HEPES, pH 7.0 (4 min, 1000×g, 23° C.), and resuspended in 4ml polystyrene round bottom tubes at a concentration of 2×10⁸tachyzoites/ml. The suspension was incubated for various times at 37° C.or treated for 15 min at 23° C. with either 1.0% (v/v) DMSO or 20 μMBAPTA-AM (1.0% [v/v] DMSO final), followed by 2 min at 37° C. with 200nM A23187 (1.0% [v/v] DMSO final) or 1.0% ethanol. Cells were pelleted(4 min, 1000×g, 4° C.) and dissolved in SDS-PAGE sample buffer.Supernatants were recentrifuged (4 min, 1000×g, 4° C.) and dissolved insample buffer. The samples were incubated for 10 min at 100° C. andanalyzed by SDS-PAGE/western blotting. Gels to be probed with either MabB3.90 or antipeptide antiserum UVT59 were run under non-reducingconditions; blots to be probed with Mab 6D10 were run under reducingconditions. The extent of parasite lysis was determined by measuring thelevels of β-galactosidase in the supernatant, as previously described[4].

Subcellular Fractionation

A subcellular fraction enriched in micronemes was prepared as described[2] except that the microneme fraction was extracted with 0.01% saponinto recover the micronemal contents.

Labeling Parasites with ¹²⁵I-iodonaphthylene azide (¹²⁵I-INA)

INA was synthesized from 5-aminonaphthalene-1-azide [11] and labeledwith ¹²⁵I (Lofstrand Laboratories, Gaithersburg, Md.) to a specificactivity of ˜1 mCi/μmol. Filtered parasites from a freshly lysedmonolayer of human foreskin fibroblasts were washed twice (1000×g, 4min, 23° C.) with IM-PR (phenol-red deficient DMEM+20 mM HEPES, pH 7.0),and resuspended in IM-PR to a concentration of 2×10⁸ tachyzoites/ml.Reduced glutathione was added to a concentration of 15 mM. Allsubsequent manipulations were performed in low light. ¹²⁵I-INA (DMSOstock, ˜1 mCi/ml) was added to the parasite suspension to a finalconcentration of 1.0% v/v DMSO. The suspension was added to an equal volof IM-PR (37° C.) containing 2.0% (v/v) ethanol in a 4 ml polystyreneround bottom tube. The cells were incubated for 2 min at 37° C.,pelleted (4 min, 1000×g, 4° C.), resuspended in IM-PR, and irradiatedfor 5 min at 4° C. using a shortwave ultraviolet lamp (UVP Inc., SanGabriel Calif.; Model UV6-54, 254 nm) at a distance of 2 cm. Theparasites were pelleted (14,000×g, 5 min) and extracted (1.4×10⁶tachyzoites/μl, 45 min, 4° C.) in 0.5% (v/v) TX-100, 50 mM Tris pH7.4,100 mM NaCl, 2 mM EDTA supplemented with 0.01 volumes of the aqueous andDMSO protease inhibitor stocks. Affinity purified polyclonal antibodyUVT59 was coupled to agarose beads and 36 μl of beads were used toimmunoprecipitate TgAMA-1 from 75 μl of the TX-100 extract as describedabove. Immunoprecipitated proteins eluted from the beads in 36 μl ofsample buffer were analyzed by SDS-PAGE under reducing conditions andwestern blotted with antipeptide antiserum as described above. Themembrane was then stripped as described above and exposed to BioMax MSX-ray film (Eastman Kodak, Rochester N.Y.) at −70° C.

Results

Identification and Initial Characterization of TgAMA-1

In experiments designed to identify novel, non-GPI-linked apical orperipheral tachyzoite antigens [3, 6], a MAb (B3.90) was generated thatreacts with a 63 kDa protein on western blots of total tachyzoiteextracts, and shows both apical and peripheral localization byimmunofluorescence (see below). MAb B3.90 recognizes a 63 kDa antigen onwestern blots of non-reduced tachyzoite extracts. No bands were detectedwhen the samples were treated with β-mercaptoethanol prior to SDS-PAGE.

In TX-114 phase partitioning experiments, the 63 kDa antigen isrecovered in the detergent phase both before and after treatment withPI-PLC, consistent with the behavior of a non-GPI-linked, transmembraneprotein. For the TX-114 phase partitioning tachyzoites (Total) wereextracted on ice in a buffer containing 0.5% (v/v) TX-114 and thecleared extract (TX-114 Soluble) was separated into aqueous (Aqueous I)and detergent (Detergent I) phases at 37° C. The detergent phase wasincubated with PI-PLC and partitioned again into aqueous (AqueousII) anddetergent (DetergentII) phases. Fractions were analyzed bySDS-PAGE/western blotting (4×10⁵ parasite equivalents loaded per lane);the 60 kDa region of a western blot was probed with MAb B3.90. SAG1, themajor GPI-linked protein of the tachyzoite, quantitatively shifted fromthe Detergent I fraction to the Aqueous II fraction under theseconditions, confirming the effectiveness of the PI-PLC treatment.

The 63 kDa antigen was purified by immunoaffinity chromatography usingMAb B3.90. Tryptic peptides prepared from the purified protein wereanalyzed by tandem microcapillary reverse-phase HPLC/ion trap massspectrometry. The resultant fragmentation spectra unambiguouslyidentified the 63 kDa antigen as Genbank entry AF010264 (deposited byHehl, Oretga-Barria and Boothroyd), the Toxoplasma homolog (TgAMA-1) ofPlasmodium AMA-1. Multiple sequence alignment of TgAMA-1 with AMA-1 fromthe different Plasmodium species revealed significant homology acrossall species. Most strikingly, 12 of the 16 cysteines whose positions areinvariant among Plasmodium species are also conserved in TgAMA-1. Thesecysteines are known to form intramolecular disulfide bridges inPlasmodium AMA-1 [12]. Other notable features in the TgAMA-1 primarysequence are a putative signal peptide, with a predicted cleavage sitebetween residues 22 and 23 (ASG-LS), and a potential transmembranedomain between residues 457 and 476.

TgAMA-1 is a Microneme Protein

To localize TgAMA-1 in T. gondii, we performed dual labelimmunofluorescence microscopy on free tachyzoites using MAb B3.90 andantibodies against known microneme (MIC2), rhoptry (ROP1), or densegranule (GRA8) antigens. In permeabilized parasites, TgAMA-1 was foundin a cap-like distribution at the apical end of the tachyzoite. Thisdistribution is indistinguishable from that of MIC2, but distinctlydifferent from that of GRA8 or ROP1, suggesting that TgAMA-1 resides inthe micronemes of T. gondii tachyzoites. Immunoelectron microscopy withMAb B3.90 supports this conclusion, as does the enrichment of TgAMA-1 ina partially purified microneme fraction.

Proteolytic Processing and Secretion of TgAMA-1

Four of the five previously identified microneme proteins (MIC1, MIC2,MIC4, MIC5) are constitutively secreted from the tachyzoite at a lowbasal rate at 37° C. [2, 4, 13]. In the case of MIC2, secretion iscoincident with specific proteolytic processing of the protein [14, 15].To determine if TgAMA-1 behaves similarly, tachyzoites were incubated at37° C. in culture medium for various times, the cells were centrifuged,and assayed by western blot to determine the amount of TgAMA-1 releasedinto the supernatant vs. the amount retained in the cell pellet. A53-k′)a fragment of TgAMA-1 was found to be constitutively secreted intothe supernatant in a time-dependent manner.

The amount of TgAMA-1 or MIC2 released from live parasites into theculture supernatant after 0 m, 10 m, 30 m, 60 m, or 120 m at 37° C. wasdetermined by western blotting is5 with either NMb B3.90 (TgAMA-1) or6D10 (MIC2). The estimated molecular masses of the secreted and cellularforms of TgAMA-1 were 53 and 63 kDa, respectively. The estimatedmolecular masses of full-length and processed forms of MIC2 are 115 kDaand 95-100 kDa, respectively [14]. The amount of TgAMA-1 (MAb B3.90) orMIC2 (MAb 6D10) released into the culture supernatant after a 2 minuteincubation at 37° C. in the presence of: DMSO (DMSO control) wasdetermined.; B-A23187 (A23187, following BAPTA-AM pretreatment); B-ETOH(ethanol, following BAPTA-AM pretreatment); A23187 (A23187, no BAPTA-AMpretreatment); or ETOH (ethanol, no BAPTA-AM pretreatment), weredetected by western blotting.

The full-length 63 kDa form, but no detectable amount of the 53-kDafragment, was 25 found to remain associated with the cell pellet. Morethan 33% of the total TgAMA-1 was found to be secreted into thesupernatant in the form of the 53-kDa fragment after 120 min at 37° C.,as estimated by comparison to serial loadings of total parasiteextracts. The extent of non-specific parasite lysis under theseconditions was determined to be less than 2%, based on the release ofsoluble β-galactosidase [4]. Thus, TgAMA-1 appears to be constitutivelyprocessed and secreted from the parasite at 37° C.

The secretion of the previously identified MIC proteins (and processingof MIC2) is enhanced by treatments which elevate intracellular calcium,including incubation with ethanol or the calcium ionophore A23187 [4,15]. The secretion of the 53-kDa fragment of TgAMA-1 was also found tobe dramatically enhanced following a 2-min treatment with ethanol orionophore A23187 this enhanced secretion was abrogated by pretreatingthe parasites with the membrane permeant calcium chelator, BAPTA-AM.

Localization and Secretion of the N- and C-Terminal Fragments of TgAMA-1

While full-length TgAMA-1 requires detergent for its solubilization, the53-kDa secreted form of the protein was recovered in the low speedsupernatant in the secretion assays, in the absence of added detergent.To test the hypothesis that the secreted fragment represents 53-kDa ofthe protein N-terminal to the putative transmembrane domain and that MAbB3.90 reacts with an epitope within this portion of TgAMA-1, wegenerated a rabbit polyclonal antiserum against a synthetic peptidecorresponding to 20 amino acids C-terminal to the transmembrane domain.The anti-peptide antibody was found to be highly specific, recognizing amajor 63 kDa band on western blots of tachyzoite extracts run undernon-reducing condition (67 kDa under reducing conditions) and a minorband of approximately 12 kDa. The anti-peptide antiserum UVT59recognized a major antigen of 63 kDa, and a minor antigen of 12 kDa onwestern blots of non-reduced tachyzoite extracts. The 63 kDaUVT59-reactive band migrated at 67 kDa under reducing conditions. The 12kDa band was not detected on identical blots probed with MAb B3.90.Proteins of 67 and 12 kDa were also immunoprecipitated with theanti-peptide antibody, and are labeled in intact parasites with thephotoactivatable hydrophobic probe ¹²⁵I-INA. Labeling of a protein with¹²⁵I-INA provides evidence that a portion of the protein is embeddedwithin a lipid bilayer [11].

The immunofluorescence pattern seen with the anti-peptide antibody wasdifferent from that seen with MAb B3.90. In methanol-permeabilizedparasites, both antibodies showed a strong concentration of TgAMA-1 atthe apical end of the parasite, superimposed on a fainter peripheraldistribution. A similar pattern was seen in parasites fixed withformaldehyde/glutaraldehyde and permeabilized with TX-100 using MAbB3.90, but under these fixation/permeabilization conditions theanti-peptide antibody labeled the periphery of the parasite with littleconcentration at the apical end. Most strikingly, 10-50% of livetachyzoites showed peripheral labeling of varying intensity with MAbB3.90, whereas no staining was seen with the anti-peptide antibody.

Taken together, these data suggest that TgAMA-1 is proteolyticallyprocessed into at least two fragments: a 53 kDa N-terminal fragmentwhich is released from the parasite and contains the epitope for MAbB3.90, and a 12 kDa C-terminal fragment which is recognized by theanti-peptide antibody and which remains associated with the parasite,presumably via its transmembrane domain. Secretion assay results areconsistent with this model: the anti-peptide antibody recognizes fulllength TgAMA-1 and the 12 kDa peptide in the cell pellet but detectsnothing in the supernatant after either 60 minutes of constitutivesecretion or 2 minutes of ethanol/A23187-induced secretion. No solublefragments of TgAMA-1 were detected with antipeptide antibody UVT59 insecretion assays. Parasites were preincubated for 2 min with or withoutBAPTA-AM, followed by a 2 min incubation in the presence of 1% ethanol.TgAMA-1 released into the assay supernatant was detected by westernblotting with MAb B3.90; the blot was then stripped and reprobed withanti-peptide antibody UVT59. Significant ethanol-induced secretion ofthe 53 kDa peptide was observed with MAb B3.90; neither this fragmentnor any other was detected in the supernatant using antipeptide antibodyUVT59.

Example 2 Expression of AMA-1 in High Five™ Insect Cells

Recombinant TgAMA-1 and various fragments of TgAMA-1 have been expressedin E. coli, but Western blotting with the conformation-sensitive MAbB3.90 suggested that these recombinant fragments were incorrectlyfolded. Proper folding of recombinant protein is more likely to beobtained in eukaryotic cell expression systems. To this end, we haverecently expressed recombinant TgAMA-1 in insect cells. Usingconventional molecular genetic techniques, Toxoplasma AMA-1 codingsequence corresponding to the signal peptide, ectodomain, and thetransmembrane domain (amino acid residues 1-473) was amplified from cDNAand ligated into pIZ/V5-His(Invitrogen) in frame with both V5 and Hiseptiope tags. PIZ/V5-His encodes a Zeocin™ resistance selectable markergene and the promoter, OpIE2, which drives constitutive expression ofthe inserted gene. The construct was transformed into E. coli andplasmid DNA was isolated from antibiotic resistant colonies. Thepresence of AMA-1 in pIZ/V5-His was confirmed by PCR, restriction digestanalysis and sequencing. High Five™ cells were transfected withpIZ/AMA-1/V5-His and stable expression was indicated by Zeocin™resistance. Antibiotic-resistant insect cell lines were cloned either bylimiting dilution or by aspirating foci; AMA-1 expression was assayed byindirect immunofluorescence microscopy using monoclonal antibody B3.90and an Alexa 488-conjugated secondary antibody. Recombinant TgAMA-1expression in insect cells was detected with mAb B3.90.

REFERENCES

References

-   [1] Wan K L, Carruthers V B, Sibley L D, Ajioka J W. Molecular    characterisation of an expressed sequence tag locus of Toxoplasma    gondii encoding the micronemal protein MIC2. Mol Biochem Parasitol    1997;84:203-14.-   [2] Carruthers V C, Giddings O K, Sibley D L. Secretion of    micronemal proteins is associated with Toxoplasma invasion of host    cells. Cellular Microbiology 1999;1:225-235.-   [3] Ward G E, Carey K L. 96-Well Plates Providing High Optical    Resolution for High-throughput, Immunofluorescence-based Screening    of Monoclonal Antibodies Against Toxoplasma gondii. J. Immunol.    Meth. 1999;230:11-18.-   [4] Carruthers V B, Sibley L D. Mobilization of intracellular    calcium stimulates microneme discharge in Toxoplasma gondii. Mol    Microbiol 1999;31:421-8.-   [5] Roos D S, Donald R G, Morrissette N S, Moulton A L. Molecular    tools for genetic dissection of the protozoan parasite Toxoplasma    gondii In: Methods in Cell Biology. 45, 1994; 27-63.-   [6] Carey K L, Donahue C G, Ward G E. Identification and molecular    characterization of GRA8, a novel, proline-rich, dense granule    protein of Toxoplasma gondii. Mol Biochem Parasitol 2000;105:25-37.-   [7] Church W R, Brown S A, Mason A B. Monoclonal antibodies to the    amino- and carboxyl-terminal domains of ovotransferrin. Hybridoma    1988;7:471-84.-   [8] Harlow E, Lane D. Antibodies: A Laboratory Manual, Cold Spring    Harbor: Cold Spring Harbor Laboratory, 1988.-   [9] Eng J K, McCormick A L, Yates J R I. An approach to correlate    tandem mass spectral data of peptides with amino acid sequences in a    protein database. Journal of the American Society of Mass    Spectrometry 1994;5:976-989.-   [10] Chittum H S, Lane W S, Carlson B A, Roller P P, Lung F D, Lee B    J, Hatfield D L. Rabbit beta-globin is extended beyond its UGA stop    codon by multiple suppressions and translational reading gaps.    Biochemistry 1998;37:10866-70.-   [11] Bercovici T, Gitler C. 5-[¹²⁵I]Iodonaphthyl azide, a reagent to    determine the penetration of proteins into the lipid bilayer of    biological membranes. Biochemistry 1978;17:1484-9.-   [12] Hodder A N, Crewther P E, Matthew M L, Reid G E, Moritz R L,    Simpson R J, Anders R F. The disulfide bond structure of Plasmodium    apical membrane antigen-1. J Biol Chem 1996;271:29446-52.-   [13] Brydges S D, Sherman G D, Nockemann S, Loyens A, Daubener W,    Dubremetz J-F, Carruthers V B. Molecular Characterization of TgMIC5,    a proteolytically processed antigen secreted from the micronemes of    Toxoplasma gondii. Molecular and Biochemical Parasitology (in    press).-   [14] Carruthers V B, Sherman G D, Sibley L D. The Toxoplasma    adhesive protein MIC2 is proteolytically processed at multiple sites    by two parasite-derived proteases. Journal of Biological Chemistry    2000;275:14346-14353.-   [15] Carruthers V B, Moreno S N, Sibley L D. Ethanol and    acetaldehyde elevate intracellular [Ca²⁺] and stimulate microneme    discharge in Toxoplasma gondii. Biochem J 1999;342:379-86.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

All references, including patent documents, disclosed herein areincorporated by reference in their entirety.

1. An isolated TgAMA-1 polypeptide molecule comprising an antigenicfragment of the polypeptide sequence set forth as amino acids SEQ IDNO:1.
 2. A fusion protein comprising the antigenic polypeptide ofclaim
 1. 3. An isolated TgAMA-1 nucleic acid molecule selected from thegroup consisting of: (a) a fragment of the nucleotide sequence set forthas nucleotides 1-2507 of SEQ ID NO:2 between 12 and 2506 nucleotides inlength, and (b) complements of (a), wherein the fragment encodes theisolated polypeptide of claim
 1. 4. An expression vector comprising theisolated nucleic acid sequence of claim 3 operably linked to a promoter.5. An expression vector comprising an isolated nucleic acid molecule ofSEQ ID NO:2. operably linked to a promoter.
 6. A host cell transformedor transfected with the expression vector of claim
 4. 7. A transgenicnon-human animal comprising the expression vector of claim
 4. 8. Thetransgenic non-human animal of claim 7, wherein the animal expresses avariable level of TgAMA-1.
 9. The transgenic non-human animal of claim7, wherein the animal expresses an antigenic fragment of SEQ ID NO:1.10. A composition comprising the isolated TgAMA-1 polypeptide of claim 1and an adjuvant.
 11. A composition comprising TgAMA-1 or a functionallyactive variant thereof, and an adjuvant.
 12. A method for immunizing asubject comprising administering to the subject an effective amount forimmunizing the subject of a composition of claim
 10. 13. The method ofclaim 12, wherein the subject is at risk of infection from Toxoplasmagondii.
 14. A TgAMA-1 binding polypeptide that selectively binds to theisolated TgAMA-1 polypeptide of claim
 1. 15. The TgAMA-1 bindingpolypeptide of claim 14, wherein the binding polypeptide is an antibodyor antigen-binding fragment of an antibody.
 16. The TgAMA-1 bindingpolypeptide of claim 15, wherein the antibody or antigen-bindingfragment specifically binds to a region comprising about 12 or morecysteine residues of the isolated polypeptide of claim
 1. 17. TheTgAMA-1 binding polypeptide of claim 14, wherein the binding polypeptideblocks entry of Toxoplasma parasite into a cell.
 18. An isolatedanti-idiotype antibody that selectively binds to the TgAMA-1 bindingpolypeptide of claim
 14. 19. A method for reducing the likelihood of ortreating a toxoplasma infection, comprising: administering to a subjectin need of such treatment, an effective amount of a TgAMA-1 bindingpolypeptide of claim 14 to treat the toxoplasma infection.
 20. Thecomposition of claim 10, wherein the composition is a proteosomevaccine.